Facile synthesis of flower shaped magnesium ferrite (MgFe2O4) impregnated mesoporous ordered silica foam and application for arsenic removal from water

Magnesium ferrite (MF0.33) impregnated flower-shaped mesoporous ordered silica foam (MOSF) was successfully synthesized in present study. MOSF was added with precursor solution of MF0.33 during MF0.33 synthesis which soaked the materials and further chemical changes occurred inside the pore. Therefore, no additional synthesis process was required for magnesium ferrite impregnated mesoporous ordered silica foam (MF0.33-MOSF) synthesis. MF0.33-MOSF showed higher morphological properties compared to other magnesium ferrite modified nanomaterials and adsorbed arsenic III [As(III)] and arsenic V [As(V)] 42.80 and 39.73 mg/g respectively. These were higher than those of other Fe-modified adsorbents at pH 7. As MOSF has no adsorption capacity, MF0.33 played key role to adsorb arsenic by MF0.33-MOSF. Data showed that MF0.33-MOSF contain about 2.5 times lower Fe and Mg than pure MF0.33 which was affected the arsenic adsorption capacity by MF0.33-MOSF. Adsorption results best fitted with Freundlich isotherm model. The possible mechanism of arsenic adsorption might be chemisorption by electrostatic attraction and inner or outer-sphere surface complex formation.


Materials and methods
All the chemicals and reagents used in present study were ACS-grade and supplied by Daihan Scientific, Republic of Korea.MgFe 2 O 4 nanomaterial was synthesized by following a method with major modifications in different experimental factors 19,20 .To follow the ratio of Fe:Mg = 0.67:0.33,appropriate amount of anhydrous ferric chloride (FeCl 3 ) and magnesium chloride (MgCl 2 ) were dissolved in 70 ml ethanol (C 2 H 6 O).After that, 10 ml of just prepared 2.03 M sodium hydroxide-ethanol (NaOH-C 2 H 6 O) mixture added to the solution.To make a homogenized solution, the mixed solution was taken under a Sonicator for 1 h at 25 ± 5 °C temperature.Sonicator probe height, amplitude and temperature were carefully maintained for all runs.The homogenized solution mixture was taken into a Teflon-line autoclave made of stainless steel and closed it tightly.Then the autoclave was kept in a convective oven for 8 h at 200 °C temperature.The autoclave was naturally cooled to room temperature.After that, the mixture was transferred into a 100 ml beaker and washed using deionized water with the help of magnetic stirrer.The washing process was continued until the mixture was free from sodium chloride.The final precipitate was transferred to a ceramic cup and taken into the oven for 12 h at 80 °C temperature.After that time period, the ceramic cup was kept in a desiccator carefully and naturally cooled.Next, the dried materials were grounded using a ceramic mortar where a dark brown finer material produced.Finally, the material was transferred into a dark glass bottle and preserved for characterization and adsorption experiments.
The method for mesoporous silica foam synthesis under present study was followed the method described by Wang et al. 21with some minor changes.At first, 1 g of P123 was measured in a beaker and kept it in a water bath having 35 °C.Then, 30 ml of 0.40 M sodium sulphate (Na 2 SO 4 ) solution was added and stirred continuously.Subsequently, 31 ml of 0.02 M sodium acetate-acetic acid buffer solution was added under continuous stirring.The mixture was stirred until a homogenous mixture solution formed.Next, 1.48 ml of tetramethyl orthosilicate (TMOS) solution was added to the solution mixture and stirred for 5 min further.The beaker containing solution mixture was kept in an incubator under 35 °C.After 24 h of incubation, the mixture was sealed in a teflon-linedautoclave and leaved it in the oven for another 24 h at 100 °C.After that, the autoclave was naturally cooled and the mixture was washed with water until it became sodium free.Finally, the white precipitate was air dried and calcined at 550 ˚C temperature for 5 h in a muffle furnace.The white colored material then was cooled in a desiccator and preserved for further analysis.
The impregnation in this study was very simple and no further chemicals were required.Appropriate amount of anhydrous FeCl 3 and MgCl 2 were mixed with synthesized MOSF in 70 ml ethanol under sonication.After 30 min of sonication, freshly prepared NaOH solution (10 ml) was added to the mixture drop wise under continuous sonication.After 1 h of sonication, the mixture was sealed in the teflon-lined-autoclave and heated at 200 °C temperature for 8 h in the oven.Next, the naturally cooled mixture was washed with deionized water for several times until the mixture was become sodium chloride (NaCl) free with the help of 2 min continuous sonication and 10 min magnetic stirring.The drying and grinding process of the washed material was same as magnesium ferrite synthesis.The magnesium ferrite nanomaterial having molar ratio of magnesium and iron 0.33:0.67 was expressed as MF 0.33 and this was incorporated into MOSF.The end material was used for characterization and adsorption process.

Adsorption experiments
To observe the adsorption efficiency of MF 0.33 -MOSF, nine sets (1, 5, 10, 25, 50, 100, 150, 200 and 300 mg/l) of As(III) and eight sets (1, 5, 10, 20, 40, 60, 100 and 130 mg/l) of As(V) concentration were prepared from stock solution (1000 mg/l).1.0 g/l adsorbent dose was applied.pH values were measured before and after adding adsorbent.Dilute hydrochloric acid (HCl) and NaOH were used to adjust pH 7 after adsorbents addition.The conical flasks containing arsenic solution and adsorbent were kept in a shaking incubator for 12 h.The incubator was operated at 300 ± 5 rpm and temperature was controlled at 25 °C.Next, the mixture solutions were centrifuged for 1 h at 4000 rpm to separate solids.Then, approximately 20 ml clear solution was transferred to plastic tube.To avoid further oxidation, 1 drop of concentrated HCl was added to each solution tube and stored.These solutions were used to determine equilibrium As(III) and As(V) concentration using inductively coupled plasma optical emission spectroscopy (ICP-OES).Adsorption capacity of synthesized MF 0.33 -MOSF nanomaterial was computed according to the equation given below 22 : where, C 0 (mg/l) is the initial concentration of As(III) and As(V), C e (mg/l) is the equilibrium concentration of As(III) and As (V), V (l) for volume, m (g) for adsorbent dose and q e (mg/g) for adsorption capacity at equilibrium respectively.
To quantify maximum arsenic adsorption capacity and possible arsenic adsorption mechanism by synthesized MF 0.33 impregnated MOSF, two adsorption isotherm models have been applied named Freundlich (Freundlich,  1906) adsorption isotherm model and Langmuir (Langmuir, 1916) adsorption isotherm model.
The Freundlich adsorption isotherm model can be expressed as follows: where, q e is the arsenic adsorption capacity by adsorbent at equilibrium (mg/g), C e is the equilibrium arsenic concentration in water (mg/l), K f (mg 1-1/n l 1/n g −1 ) and n is the Freundlich empirical constants which are related to the maximum arsenic adsorption and the 1/n is the heterogeneity factor of the nanoadsorbent representing the strength of adsorption.The value of n should be lie between 1 and 10 for favorable adsorption process 23 .
The Langmuir adsorption isotherm model can be expressed as follows: where, K L (l/mg) designated as Langmuir adsorption constant, C e is the equilibrium arsenic concentration (mg/l), q e (mg/g) is the arsenic adsorption capacity at equilibrium and q m (mg/g) represents maximum adsorption capacity of As(III) and As(V) on MF 0.33 -MOSF.The affinity of arsenic toward binding site is related with K L .

Determination of pH PZC
Point of zero charge (pH PZC ) of MF 0.33 -MOSF nanomaterial was identified through pH Drift method 24 .In short, based on pH, 10 different sets of vial (pH 3-12) were prepared by adding 15 ml NaCl solution having 0.1 M concentration.pH 3-12 was made by using HCl or NaOH solutions (for pH ˂ 7, HCl and for pH ˃ 7, NaOH).Subsequently, 0.015 g of MF 0.33 -MOSF nanomaterial was added to each vial.The vials were stirred 4 h using a magnetic stirrer and kept it in a temperature (25 °C) controlled incubator for 24 h.The final pH of each vials were measured and an initial pH vs pH change (ΔpH) graph was made.The line pH-ΔpH crossed the point of pH zero line is the pH PZC of the material.

Ethical approval
This is an original research and has not been submitted elsewhere at the same time.The whole research compiled in a single manuscript which submitted to Scientific Reports.A new material named MOSF modified MF was first time prepared and applied for arsenic removal by the authors.Before submission, the manuscript was checked for plagiarism using Turnitin software.

Results and discussion
Characteristics of magnesium ferrite impregnated MOSF

XRD
The XRD spectra of synthesized MF 0.33 , MOSF and MF 0.33 -MOSF material at 2θ scale ranging from 10° to 80° were shown in Fig. 1.For MOSF, only one peak was found at 2θ = 22° on the XRD spectra which was representative for the formation of amorphous silica 25 .The peak pattern found in MF 0.33 demonstrated successful synthesis of single phase [S/M (PDF-2 release 2020 RDB)] cubic shape magnesium ferrite spinels which belongs to space group Fd3m (227:Fd-3 m:2; a = 8.39913 Å).Therefore, based on the comparison results, the new synthesized material contained both amorphous silica phase and magnesium ferrite spinels.These data also confirmed that magnesium ferrite crystals were well established in MOSF structure.Intense peaks of the XRD plane were used to calculate average crystallite size according to Debye-Scherrer's formula 26,27 .
According to the Debye-Scherrer's formula, www.nature.com/scientificreports/where, D (nm) average crystalline size, K (K = 0.89) is considered as Scherer's constant, λ (Å) represents the applied wavelength of X-ray, β (radian) represents as the full width at half maximum (FWHM) of the diffraction peak and θ represents diffraction angle produced by the peak.The calculated average crystallite size was found 5.85, 0.75 and 1.84 nm for MF 0.33 , MOSF and MF 0.33 -MOSF respectively.There were no other peaks found on the XRD plane which confirmed that the material synthesized under present research is in single phase state with high purity.
N 2 adsorption-desorption isotherms Specific surface area, average pore volume and pore size of MF 0.33 , MOSF and MF 0.33 -MOSF were measured through N 2 adsorption-desorption isotherm analysis, as represented in Fig. 2. Comparing with international union of pure and applied chemistry (IUPAC) provided classification of hysteresis loop, the pattern displayed in N 2 adsorption-desorption curves were matched with single mode IV which belongs to H1 hysteresis loop.Based on IUPAC classification, this type of hysteresis mode corresponding to the presence of abundant mesoporous pores 28 .The Barrett-Joyner-Halenda (BJH) pore size distribution pattern revealed average pore diameter of MF 0.33 , MOSF and MF 0.33 -MOSF were 4.17, 11.41 and 6.05 nm respectively (Table S1).MF 0.33 impregnation in MOSF decreased the pore diameter, which might be resulted from the incorporation of MF 0.33 particles in pore of MOSF.The Brunauer-Emmett-Teller (BET) total pore volume and specific surface area of mesoporous MF 0.33 , MOSF and MF 0.33 -MOSF nanomaterials were 0.2083, 0.8012, 0.4684 cm 3 /g and 200.36, 412.86, 427.04 m 2 /g respectively.Owing to impregnation, BET surface area was increased, which indicated that the particles size of www.nature.com/scientificreports/MF 0.33 -MOSF was decreased after impregnation.The average nanoparticle size found by BET analysis (29.95, 14.53 and 14.05 for MF 0.33 , MOSF and MF 0.33 -MOSF respectively) also supported the increment of surface area.The decrease in total pore volume in impregnated material might be also resulted from the impregnated magnesium ferrite in MOSF.Therefore, the MF 0.33 -MOSF nanomaterial showed exceptionally large surface area, high pore volume and mesoporous pore size that would be an efficient adsorbent for pollutant removal from water.

FTIR
To recognize the bonding types, nature and functional groups of the MF 0.33 , MOSF and MF 0.33 -MOSF nanomaterials, FTIR analysis was performed and results showed in Fig. 3.The IR data was collected in range of 400-4500/ cm of wavenumber.The distinctive adsorption peaks of MF 0.33 nanomaterial were appeared at 3416, 1637, 1384, 1034, 590 and 433/cm region were identical to the literature data for magnesium ferrite nanomaterial 14,29 .The broader peak appeared at 3416/cm and the sharp peak turned up at 1637/cm region were associated with stretching and bending vibrations of -O-H groups and surface adsorbed water (H 2 O) by hydrogen bond on MF 0.33 surface.The other sharp peaks produced at 1384/cm and 1034/cm region of the spectra were assigned to deformation and bending vibrations of metal hydroxide (M-OH − ), which coordinated to Fe 3+ or Mg 2+ .The intense peaks appeared at 590/cm and 433/cm were related to the innate vibrations of octahedral and tetrahedral metal oxides (M-O) 29 .For MOSF, the peak at 3434/cm was attributed to stretching vibration of -OH on the MOSF surface.The bending vibration of the adsorbed water on the surface absorbed the light 1629/cm.Additionally, the peak at 1091/cm and 810/cm were attributed to asymmetric and symmetric stretching vibrations of Si-O-Si bond.Furthermore, the peak produced at 465/cm was assigned to the structural SiO 4 tetrahedra 30,31 .The FTIR www.nature.com/scientificreports/spectra for MF 0.33 -MOSF nanomaterial showed almost all the chemical bonds observed in MF 0.33 and MOSF.These results also confirmed the successful impregnation of MF 0.33 in MOSF.

SEM-EDS
Surface morphology of MF 0.33 , MOSF and MF 0.33 -MOSF nanomaterials were observed through SEM analysis (Fig. 4).The synthesis method of MF 0.33 and MF 0.33 -MOSF nanomaterial was divided into four steps which were homogenization, thermal treatment, washing and drying.The synthesized materials after thermal treatment remain as finer particles which suspended rapidly in water during washing of the material for NaCl removal.However, the nanomaterials formed small agglomerates after 12 h heating in the oven for drying.Therefore, naturally cooled agglomerates were taken into a ceramic mortar and grounded to finer particles.The SEM image www.nature.com/scientificreports/ of MOSF nanomaterials was showed flower shape in appearance and there was no need to grind.Because of grounding, the agglomerates of MF 0.33 were broken through the boundary line between the cubic spinel shape particles which were shown in Fig. 4. Although, the impregnated material showed similar agglomerates like MF 0.33 but clear spinels could not be found in the impregnated materials like MF 0.33 which might be due the growth of MF 0.33 spinels inside the pores of flower shape MOSF nanomaterial.This also supported the data found in N 2 adsorption-desorption isotherm analysis.Based on that data, the MOSF nanomaterial was found mesoporous having large pores.And it was also found that the size of MOSF particles were smaller than that of MF 0.33 .After impregnation, the pore size and pore volume of MOSF nanomaterial decreased and a new shape was found in MF 0.33 -MOSF image which has similarities with flower shape MOSF.
For the evaluation of elemental composition in each nanomaterial, EDS analysis has been done (Fig. 4).The EDS analysis of MF 0.33 -MOSF proved the presence of Si, Fe, Mg and O element, which came from MF 0.33 and MOSF.The MF 0.33 nanomaterial contains 23.10% of Fe and 11.55% (atomic weight base) of Mg.But after impregnation of MF 0.33 in MOSF by 1:1 ratio, MF 0.33 -MOSF contain approximately 2.37 times lower Fe and 2.67 times lower Mg than MF 0.33 .This lower amount of Fe and Mg in MF 0.33 -MOSF might affect the adsorption capacity of the impregnated material.EDS result also showed that there were no other element presents in the synthesized material, which confirmed phase purity of the nanomaterials.These results confirmed that the phase pure MF 0.33 impregnated MOSF nanomaterial had been successfully synthesized in present study.

VSM
Magnetic properties of synthesized MF 0.33 and MF 0.33 -MOSF nanomaterials were analyzed by vibrating sample magnetometer (VSM) at room temperature with an application of magnetism of − 20,000 to 20,000 Oersted (Oe) (Table S2).The magnetic saturation (Ms), retentivity (Mr) and coercivity (Hc) were found 16.90 emu/g, 1.30 emu/g, 30.15Oe for pure MF 0.33 and 1.36 emu/g, 0.14 emu/g, 153.14 Oe for MF 0.33 -MOSF from VSM data respectively.Pure MgFe 2 O 4 phase showed S-shaped magnetization curve (Fig. 5), which indicated that MF 0.33 was superparamagnetic material and can be separated easily by an external magnet after adsorption.Conversely, MOSF is a non-magnetic material.After impregnation of MF 0.33 in MOSF, the new material showed week magnetic properties.
Magnetization saturation of the synthesized nanomaterials was calculated using the formula: where, mS is the saturation moment of a single particle and φ is the volume fraction, it is clear that Ms can be determined by volume fractions and intrinsic properties (saturation moment) of materials involved.Thus, low magnetism of MF 0.33 -MOSF can be attributed to low amount of incorporated MF 0.33 in it 32 .The magnetic properties decreased after impregnation but magnetic properties of the MF 0.33 -MOSF could be tuned by controlling these two parameters.Coercivity depends on particle size which will increase up to certain limit with decreasing particle size 33 .Based on BET data, particles size of MF 0.33 was found 29.95 nm and after impregnation, particle size was 14.05 nm for MF 0.33 -MOSF.Therefore, coercivity increased in MF 0.33 -MOSF than MF 0.33 .The remnant magnetization (Mr) is the magnetization left after removing external magnetic field from a material.The Mr value was found 1.30 emu/g for pure MF 0.33 and 0.14 emu/g for MF 0.33 impregnated MOSF.Superparamagnetic MF 0.33 showed 9.29 times higher Mr than MF 0.33 -MOSF.The ratio of Mr and Ms is called squareness which is important properties for ferromagnetic materials.Depending on processing, Mr/Ms ratio of commercial magnets varied in the range 0.88-0.96 34.The squareness ratio were found 0.08 and 0.10 for MF 0.33 and MF 0.33 -MOSF.Because of cubic spinel shape, MF 0.33 has less Mr/Ms which increased impregnated material.

Comparative study of morphological characteristics
Magnesium ferrite impregnated mesoporous ordered silica foam has been synthesized for the first time under present study.The modified magnesium ferrite nanomaterial showed exceptionally large surface area compared to other modified magnesium ferrite nanomaterials found in literature till date (Table S3).Tiwari and Kaur 36 , synthesized silica@magnesium ferrite [SiO 2 @MgFe 2 O 4 ] material having higher surface area and pore volume than MF 0.33 -MOSF synthesized in this research.But the pore size of SiO 2 @MgFe 2 O 4 material approximately 1.71 times lower than MF 0.33 -MOSF.In addition, complex synthesis process was involved in SiO 2 @MgFe 2 O 4 synthesis.At first they synthesized SiO 2 and MgFe 2 O 4 nanomaterial.After that further synthesis process was involved for SiO 2 @MgFe 2 O 4 synthesis 36 .Whereas, the synthesis of MF 0.33 -MOSF material was very much simple in present study.At first MOSF synthesized and then this MOSF mixed with other precursor solutions during MF 0.33 synthesis.Therefore, no further synthesis steps were involved, which could save energy and cost of the research.So, present research successfully synthesized MF 0.33 -MOSF nanomaterial through a simple and cost effective way having large pore size, pore volume and surface area compared to other nanomaterials found in literature (Table S3).

Arsenic adsorption capacity
Adsorption isotherm Table S4 showed the equilibrium arsenic adsorption isotherm results.The adsorption of both As(III) and As(V) species on synthesized MF 0.33 and MF 0.33 -MOSF nanomaterial were tried to fit in Langmuir and Freundlich isotherm model (Fig. 6).The fitting results showed that adsorption data was best fitted on Freundlich model based on coefficient of correlation (r 2 ) data.According to Foo and Hameed 37 , Langmuir adsorption isotherm is an www.nature.com/scientificreports/equation based on monolayer adsorption of adsorbate onto adsorbent surface.Besides, Freundlich adsorption isotherm model is based on multilayer adsorption of adsorbate onto heterogeneous surface of the adsorbent which is not restricted to monolayer formation 37,38 .Therefore, multilayer adsorption of both arsenic species was taken place on MF 0.33 and MF 0.33 -MOSF heterogeneous surface.The heterogeneity factor, 1/n can be found from Freundlich model.The value 0.1 ˂ 1/n ˂ 1 describes efficient adsorption of adsorbate on adsorbent surface 39 .In present study, the parameter 1/n calculated from Freundlich model were found 0.34, 0.32 by MF 0.33 and 0.40, 0.63 by MF 0.33 -MOSF for As(III) and As(V) adsorption, which indicated that both species adsorbed easily on MF 0.33 and MF 0.33 -MOSF surface 40 .
The maximum arsenic adsorption capacity of MF 0.33 and MF 0.33 -MOSF nanomaterial was found in Langmuir isotherm model.Based on model results, MF 0.33 and MF 0.33 -MOSF adsorbed 103.94, 42.80 mg/g of As(III) and 45.52, 39.73 mg/g of As(V) at pH 7 respectively.With increasing initial arsenic concentration, adsorption capacity was also increased.At equilibrium, MF 0.33 nanomaterials adsorbed approximately 2.4 times higher amount of As(III) than MF 0.33 -MOSF.For As(V) adsorption, MF 0.33 adsorbed slightly higher amount than MF 0.33 -MOSF.As the MOSF showed no arsenic adsorption capacity, MF 0.33 was totally responsible for arsenic adsorption.Besides that, based on EDS results, MF 0.33 -MOSF contained 2.37 times lower Fe and 2.67 times lower Mg than MF 0.33 when MF 0.33 -MOSF was synthesized in 1:1 ratio of MF 0.33 and MOSF.Elemental analysis data by ICP-OES also showed that MF 0.33 -MOSF contain 2.47 times lower Fe and 2.42 times lower Mg than pure MF 0.33 .Therefore, the lower arsenic adsorption capacity was due to lower Fe and Mg content in MF 0.33 -MOSF nanomaterial, which could be enhanced by changing the MF 0.33 and MOSF ratio.

Adsorption mechanism
Arsenic adsorption on MF 0.33 -MOSF nanomaterial can be discussed based on isotherm data and pH PZC of the material.Adsorption results were well fitted to Freundlich isotherm model indicating that arsenic adsorption occurred on heterogeneous surface of MF 0.33 -MOSF nanomaterial.Therefore, possible mechanism of arsenic adsorption might be through physisorption and chemisorption.In addition, the pH PZC of MF 0.33 -MOSF was found 9.02 which indicated that the nanomaterial surface was positively charged at pH 7 (pH ˂ pH PZC ).The available forms of As(III) and As(V) under pH 7 are H 3 AsO 3 , H 2 AsO 4 -and HAsO 4 2-which might be easily adsorbed on MF 0.33 -MOSF surface through electrostatic attraction, ion exchange and complex formation.There were two pH PZC (3.31 and 4.78) found for pure MOSF material (Fig. 7).Chrzanowska et al. 41 found pH PZC 4-5.6 of pure mesocellular silica foam.Derylo-Marczewska et al. 42 found pH PZC 4.93 of pure mesoporous silica foam which changed to 6.5 after protein adsorption.Brönsted acidity in silica surface is a well-known properties and pH PZC of these materials was found at a range 2-3 which indicated that silica surface have positive charge (pH ˂ pH PZC ) at very lower pH.In addition, after coating with magnetite the pH PZC of modified mesoporous silica changed to 8 which generated positive silica surface 43   Considering above reactions, chemisorption was the dominant adsorption mechanism for As(III) and As(V) adsorption.Chemisorption process occurred through complex formation, ion exchange and electrostatic attraction.The literature data regarding arsenic oxyanions adsorption on spinal ferrites revealed that the dominant adsorption mechanism was surface complex formation 1,18,38,[44][45][46] .

Comparison with other adsorbents for arsenic adsorption
For the first time, magnesium ferrite was impregnated in MOSF which showed enhanced surface area, mesoporous pore size and high pore volume.The material was applied as adsorbent for arsenic removal at pH 7 and 25 °C.The maximum As(III) and As(V) adsorption capacity were found 42.80 and 39.73 mg/g respectively.The material adsorbed higher amount of As(III) and As(V) from water compared to other adsorbents listed in Table S5 at pH 7.
Fe modified activated carbon material showed lower As(III) and As(V) adsorption capacity 4,47 .In addition, longer equilibrium time and membrane filtration with N 2 purging applied for adsorption which limited the research for further application in water treatment.Gupta and Ghosh 48 synthesized Fe(III)-Ti(IV) binary oxide which removed 85 mg/g As(III) within 4.5 h at pH 7.However, the material removed very much lower amount (14 mg/g) of As(V) within 7.5 h at pH 7. In addition, they maintained pH for certain time period until equilibrium reached during adsorption.Furthermore, membrane filtration was applied for separation of adsorbent from water 48 .Fe 3 O 4 -MnO 2 binary oxide adsorbed 32.13 mg/g As(V) at pH 5 49 .Yu et al. 6 synthesized cellulose@Fe 2 O 3 magnetic composites and applied for arsenic removal.The nanocomposites adsorbed 23.16 mg/g As(III) at pH 7.5 and 32.11 mg/g As(V) at pH 2. 3D organized mesoporous silica coated with Fe and Al oxide was synthesized by Glocheux et al. 50which adsorbed 55 mg/g As(V) at pH 5 and 35 mg/g As(V) at pH 4 respectively.Fe 2 O 3 / SiO 2 nanocomposite adsorbed only 21.50 mg/g As(III) at pH 7.5 and 14.90 mg/g As(V) at pH 4.5.In both cases, adsorption temperature was 35 °C51 .Ahangari et al. 52 synthesized nickel-zinc ferrite modified carbon nanotubes nanocomposite for As(V) removal from wastewater.The nickel-zinc ferrite (NZF) and carbon nanotube nickelzinc ferrite (CNZF) nanocomposites adsorbed 56 and 66 mg/g As(V) at pH 2 and 6 g/l of adsorbent dosage 52 .Therefore, comparing with activated carbon, carbon nanotube, cellulose, binary oxides and other silica modified nanomaterial/nanocomposites, MF 0.33 -MOSF found efficient adsorbent material for As(III) and As(V) removal from water.
Furthermore, magnesium ferrite impregnated MOSF was synthesized following MF 0.33 synthesis process where MOSF added with precursor materials of MF 0.33 therefore, no further synthesis process had been applied.For synthesis of other modified materials (Table S3), complex synthesis process were involved which needed higher energy, time and cost.Therefore, based on synthesis, characteristics and adsorption capacity, MF 0.33 -MOSF nanomaterial was considered as one of an ideal material for water treatment.This nanomaterial might work as a green material for sustainable water treatment technology development in future.

Conclusion
Iron based nanomaterials have drawn much attention in adsorptive removal of pollutants from water because of their availability, properties, adsorption capacity, lower cost and ecofriendly nature.Among them, magnesium ferrite nanomaterials showed greater properties and performance in water treatment process.However, being a nanomaterial, it has limitations such as stability, aggregate formation and separation.Therefore, modification of magnesium ferrite nanomaterials with well-structured materials having higher stability, surface area and easy separation from solution are very much popular in recent time.Following that, a new combination, MF 0.33 -MOSF has been successfully synthesized and applied for As(III) and As(V) removal from water at pH 7. MOSF having negatively charged surface area at pH 7 showed repulsion against arsenic oxyanions.However, adsorption properties were increased after impregnation with MF 0.33 .The magnetic MF 0.33 -MOSF showed better morphological properties and adsorption capacity (at pH 7) compared to other nanomaterials found in literature.Adsorption results best fitted with Freundlich isotherm and adsorption mechanism was found to chemical sorption through complex formation and electrostatic attraction on heterogeneous surface.Modification of MF 0.33 with MOSF using simple, less time-consuming and cost-effective procedure was successfully confirmed to be effective.Therefore, magnetic MF 0.33 -MOSF composites could be competitive nanoadsorbents for arsenic removal from water. https://doi.org/10.1038/s41598-023-48327-7

MF
17w.nature.com/scientificreports/goodmagneticpropertiesaftercompositeformationwith superparamagnetic MgFe 2 O 4 that can be separated easily from water by a magnet35.Khafagy32showed that magnetization of pure phase MgFe 2 O 4 decreased (21.33-5.905emu/g)whencoating MgFe 2 O 4 with polyaniline.They also found that coercivity decreased 88.66 Oe-81.60 Oe after coating because the particle size of pure MgFe 2 O 4 (30-35 nm) increased (45 nm) after coating.Hoijang et al.17synthesized silica-coated MgFe 2 O 4 showing superparamagnetic properties.The magnetization of pure MgFe 2 O 4 and silica-coated MgFe 2 O 4 were found 37 and 27 emu/g.During synthesis, they added only 1 ml tetraethyl orthosilicate in a solution containing 200 mg of MgFe 2 O 4 .Because of higher amount of MgFe 2 O 4 , the magnetic properties was not decreased much.Therefore, magnetic properties of the nanomaterials synthesized in present study could be increased by changing MF 0.33 and MOSF ratio.